1. Field of the Invention
The present invention relates generally to weight measuring devices. More particularly, the invention concerns a method and apparatus for determining the weight of the contents of a vessel at selected time intervals.
2. Discussion of the Invention
It has been a common practice in the past to use load cells for measuring the weight of various types of articles or materials, such as those contained within vessels and hoppers. Such measurements have typically been accomplished through the use of load cells that are positioned beneath the legs of the article to be weighed. Because the load cells and their mounting hardware support the entire vessel and contents, the load cells are unduly expensive. Further, in order to install the load cells, the vessel or hopper must generally be raised a substantial distance and, in many instances, the legs of the tank or hopper must be cut or otherwise structurally modified in order to install the load cells. This approach can result in time delays and substantial expenditures of both time and money.
Another prior art approach sometimes used for measuring the weight of articles or materials contained within supporting structures involves the use of strain gage devices that are mounted within drilled holes formed in the structural members of the supporting structure. In such instance, the strain gages are adapted to measure the deformation of the hole in the structural member as the load is increased. Typically the installation of such strain gage devices is difficult and the reliability of such measurements are frequently suspect.
To overcome the drawbacks of prior art measuring systems of the character described in the preceding paragraphs, the present inventor developed a novel clamp-on structural strain gage sensor that can be mounted to dynamic load bearing structures such as sucker-rod type oil well pumps to produce an electrical output proportional to the deflection of the structures. This novel strain measuring apparatus is disclosed in U.S. Pat. No. 5,423,224 issued to the present inventor. Because of the pertinence of this patent to an understanding of the present invention, the patent is hereby incorporated by reference as though fully set forth herein.
In one embodiment of the invention described in U.S. Pat. No. 5,423,224 invention, the strain measuring apparatus of the invention can be used in conjunction with conventional weighing instrumentation such as a Weigh Meter and has the ability to convert the analog signal to a digital signal for processing and correction and then to reconfigure the data back to analog signals for input to the Weigh Meter.
As will be better understood from the discussion of which follows, the method of the present invention involves the installation of a thin, yieldably deformable, elastomeric pad under each leg of the vessel and then, as matter is either added to our taken from the vessel, measuring the deflection in the elastomeric pads using a sensor means that are conveniently mounted above the flanges that are affixed to the vessel support base and support the legs. This unique approach does not require any cutting or modification of the supporting legs and requires only that the vessel flanges be lifted above the support base a limited distance to accept the pads. Additionally, because only the deflection of elastomeric material beneath the legs is being measured the transducers can be small and quite inexpensive.
It is an object of the present invention to provide a method and apparatus for accurately determining the weight of the contents of a vessel at selected time intervals.
Another object of the invention is to provide a method of the aforementioned character that can be used as an inventory control technique for inventorying the contents of the vessel at any given time.
Another object of the invention is to provide an apparatus of the character described that can be quickly and easily installed on an existing structure without requiring substantial modification to the structure.
Another object of the invention is to provide an apparatus which embodies small and inexpensive transducers for determining the weight of the contents of the vessel.
Another object of the invention is to provide an apparatus of the character described in the preceding paragraphs in which the transducers are conveniently mounted above the flanges that support the vessel legs.